class_docstr: Keep track of and clean up after modules created while building Bokeh
  Documents.
code: def __len__(self) -> int:
      return len(self._modules)
  
file_path: bokeh/src/bokeh/document/modules.py
imports: from __future__ import annotations
  import logging
  import sys
  import weakref
  from types import ModuleType
  from typing import TYPE_CHECKING
label_desc: Use image node_id 2 for calling the DocumentModuleManager obj's underlying member method code with example usage: obj.__len__() and returns: len